Field of the Invention
[0001] The invention relates to a method for processing high contrast silver halide photographic
materials.
Background of the Invention
[0002] The vast majority of commercially available developers for black and white films
are based on hydroquinone. However, the use of hydroquinone is suspect from an ecological
point of view. It can have allergic effects and some countries are proposing to list
hydroquinone as a suspect carcinogen. Developing agents not showing these disadvantages
are ascorbic acid and related compounds [see, for example, P. Meeuws
et al., (Agfa Gevaert),
Research Disclosure, March 1995, p. 185].
[0003] Ascorbic acid has been recognised as a developing agent for some time, and, although
less active than hydroquinone or catechol, the photographic literature reports it
will develop a conventional emulsion at high pH [see, for example, W.E. Lee and E.R.
Brown in The Theory of the Photographic Process, 4th ed., ed. T.H. James, Macmillan,
New York and London, 1977, chapter 11]. However, the number of instances of the commercialisation
or useful employment of an ascorbic acid-based developer are relatively few. An ascorbic
acid-based developer suitable for hydrazine containing high contrast films has been
described in US Patent No. 5,236,816. Also, US Patent No. 5,474,879 describes an ascorbic
acid developer particularly suitable for radiographic films.
[0004] For many years the very high contrast photographic images needed in the graphic arts
and printing industries were obtained by developing a "lith" emulsion (usually high
in silver chloride content) in a hydroquinone, low sulphite, "lith" developer by a
process known as infectious development. High contrasts were achieved. However, such
low sulphite developers are inherently unstable and are particularly inappropriate
for machine processing.
[0005] Machine processing of graphics materials was achieved by the use of so-called "rapid
access" high contrast materials which have a lower scale (or toe) contrast below 3
and typically about 2, good process latitude and good process stability. Such materials
are easy to use but this is at the expense of noticeably reduced dot quality (i.e.
a so-called "soft" dot) and hence are not suitable for users requiring the highest
of dot qualities. Rapid access film materials are, however, widely accepted and used
and are in daily use alongside nucleated products described immediately below.
[0006] To achieve the high image quality obtainable from lith processing but with a stable
process, emulsions containing nucleating agents, for example hydrazides, have been
used and processed in a high pH (~ 11.5) developer with conventional amounts of sulphite,
hydroquinone and co-developer. A further refinement in the area of high contrast materials
was the introduction of a lower pH process (typically ~10.4) using hydrazides active
at this pH together with the use of an incorporated contrast booster compound, such
as an amine. Both these processes provide half-tones with a so-called "hard" dot.
[0007] However, such materials incorporating nucleators and booster compounds are not ideally
desirable because the process sensitivity is still substantially worse than that obtained
with the rapid access process.
[0008] The infectious process phenomenon of "co-development" [R. Beels and F.H. Claes,
The Journal of Photographic Science, 1975,
22, 23] is defined as the tendency for unexposed silver halide grains with no latent
image to develop if they are in the near vicinity of developing grains which are fogged.
No spectral sensitisation is described. The extent of the co-development reported
has been insufficient to make this little more than an interesting observation.
[0009] EP-A-0 758 761 discloses that when an imagewise exposed silver halide layer having
both spectrally sensitised and non-spectrally sensitised silver halide grains, a high
silver:gel ratio, and containing an appropriate amine, its density can be enhanced
by the co-development effect to give a substantial density gain enabling the production
of a high contrast photographic material which does not contain a nucleating agent.
Advantages of the enhanced co-development film were cited to be: the lack of a nucleating
agent and the use of less silver, gelatin and sensitising dye to obtain improved contrast/image
quality, lower post-process dye stain through reduced dye laydown and reduced cost.
In addition the absence of nucleating agents meant the film was free of so-called
"pepper fog".
Problem to be solved by the Invention
[0010] Although efficacious, the use of enhanced co-development films has some limitations
and drawbacks. In spite of the fact that such materials are relatively process insensitive
in hydroquinone-based developers, there remains some process sensitivity which it
would be advantageous to reduce or eliminate.
[0011] Additionally, in hydroquinone-based developers where, through poor process management,
the pH has been allowed to fall below 10.0 and towards 9.5, the dot quality becomes
less acceptable, with ragged high contrast edges which do not give good results on
contacting to, for example, a contact film or printing plate.
[0012] Finally, at pH values of 10.0 or lower there appears in non-image areas a development
of silver specks which are considered to be undesirable.
Summary of the Invention
[0013] A method of forming a photographic image in an imagewise exposed high contrast photographic
material free from nucleating agents comprising a support bearing a silver halide
emulsion layer comprising silver halide grains wherein at least 10% of the silver
halide grains are spectrally sensitised and a hydrophilic colloid having a silver:hydrophilic
colloid ratio above 1, the method comprising developing the material in a developer
comprising an ascorbic acid developing agent at a pH no greater than 10.5, the developer
being free of hydroquinone.
Advantageous Effect of the Invention
[0014] The combination of the co-development photographic material and an ascorbic acid-based
developer allows for all the previous advantages of the material to be retained, such
as a reduction in the amount of sensitising dye used compared to conventional graphics
films thus providing low post-process dye stain and lower product cost, while extending
to it the ability to obtain a high contrast result with an ecologically advantageous
developer. Unexpectedly, the combination allows process insensitivity greater than
that obtained with conventional hydroquinone-based developers. In addition the dot
quality from the enhanced co-development photographic material in the ascorbic acid-based
developer does not deteriorate as the pH falls. Finally, the unwanted development
of silver specks in unexposed areas of the photographic material is significantly
and surprisingly reduced by the method of the invention compared against the method
in which the same material is developed in a hydroquinone-based developer.
Brief Description of the Drawings
[0015]
Figures 1 to 6 are D-LogE curves showing the sensitometric results obtained from processing
photographic materials according to Example 1 below.
Figures 7 to 10 are magnified images of 50% written half-tone dots produced by processing
photographic materials according to Example 3 below.
Detailed Description of the Invention
[0016] An ascorbic acid developing agent includes ascorbic acid and the analogues, isomers
and derivatives thereof which function as photographic developing agents. Ascorbic
acid developing agents are known in the photographic art and include the following
compounds: L-ascorbic acid, D-ascorbic acid, L-erythroascorbic acid, D-glucoascorbic
acid, 6-desoxy-L-ascorbic acid, L-rhamnoascorbic acid, D-glucoheptoascorbic acid,
imino-L-erythroascorbic acid, imino-D-glucoascorbic acid, imino-6-desoxy-L-ascorbic
acid, imino-D-glucoheptoascorbic acid, sodium isoascorbate, L-glycoascorbic acid,
D-galactoascorbic acid, L-araboascorbic acid, sorboascorbic acid and sodium ascorbate.
[0017] L-ascorbic acid and sodium isoascorbate are preferred developing agents.
[0018] The developing composition can also include one or more auxiliary super-additive
developing agents as are known in the art (Mason,
Photographic Processing Chemistry, Focal Press, London, 1975), that is to provide a synergistic effect whereby the
combined affect of a mixture of two developing agents is greater than the sum of the
individual activities. The aminophenols and 3-pyrazolidones are preferred as such
components with the last type of compound being more preferred.
[0019] Particularly preferred auxiliary developing agents are disclosed in US-A-5,457,011
including 1-phenyl-3-pyrazolidone, 1-phenyl-4,4-dimethyl-3-pyrazolidone, 1-phenyl-4-methyl-4-hydroxymethyl-3-pyrazolidone
and 1-phenyl-4,4-dihydroxymethyl-3-pyrazolidone. Other useful 3-pyrazolidone developing
agents include 1-phenyl-5-methyl-3-pyrazolidone, 1-phenyl-4,4-diethyl-3-pyrazolidone,
1-p-aminophenyl-4-methyl-4-propyl-3-pyrazolidone, 1-p-chlorophenyl-4-methyl-4-ethyl-3-pyrazolidone,
1-p-acetamidophenyl-4,4-diethyl-3-pyrazolidone, 1-p-betahydroxyethylphenyl-4,4 dimethyl-3-pyrazolidone,
1-p-hydroxyphenyl-4,4-dimethyl-3-pyrazolidone, 1-p-methoxyphenyl-4,4-diethyl-3-pyrazolidone
and 1-p-tolyl-4,4-dimethyl-3-pyrazolidone.
[0020] Useful aminophenols include p-aminophenol, o-aminophenol, N-methylaminophenol, 2,4-diaminophenol
hydrochloride, N-(4-hydroxyphenyl)glycine, p-benzylaminophenol hydrochloride, 2,4-diamino-6-methylphenol,
2,4-diaminoresorcinol and N-(β-hydroxyethyl)-p-aminophenol.
[0021] More than one primary developing agent can be used in the developing compositions
used in this invention. For example, the developing composition can contain two different
ascorbic acid developing agents. More than one auxiliary super-additive developing
agent can be included in the developing compositions. For example, the developing
compositions can contain two different aminophenol developing agents or two different
3-pyrazolidone developing agents or both an aminophenol developing agent and a 3-pyrazolidone
developing agent.
[0022] It is preferred that the method of the invention comprises developing the material
in a developer based on ascorbic acid which is free of any dihydroxybenzene developing
agent.
[0023] The primary developing agent is present in the working strength developing composition
in a conventional amount, that is a least 0.05 mol/l, and preferably at least 0.1
mol/l. The upper limit is generally 1 mol/l, and preferably 0.5 mol/l. The auxiliary
super-additive developing agent is generally present in the working strength solution
of developing composition in an amount of at least 0.001 mol/l, and preferably at
least 0.002 mol/l. The upper limit of such compounds is 0.1 mol/l, and preferably
0.01 mol/l.
[0024] It is preferred that the processing composition includes one or more sulphite preservatives.
By "sulphite preservative" is meant any sulphur compound that is capable of forming
sulphite ions in aqueous alkaline solution. Examples of such compounds include alkali
metal sulphites, alkali metal bisulphites, alkali metal metabisulphites, sulphurous
acid and carbonyl-bisulphite adducts. Examples of preferred sulphites include sodium
sulphite, potassium sulphite, lithium sulphite, sodium bisulphite, potassium bisulphite,
lithium bisulphite, sodium metabisulphite, potassium metabisulphite and lithium metabisulphite.
The carboyl-bisulphite adducts that are useful as sulphite preservatives are described,
for example, in US-A-5,457,011.
[0025] The amount of sulphite preservative used in the working strength processing compositions
can vary widely, but generally it is present in an amount of at least 0.05 mol/l,
and preferably at least 0.1 mol/l. The upper limit is genrally 1.0 mol/l, and preferably
0.5 mol/l.
[0026] The processing compositions, when used in working strength, generally have a pH of
from about 9.0 to about 10.5, and preferably from about 9.5 to about 10.0. Suitable
buffers, such as carbonates, borates and phosphates can be used to provide or maintain
the desired pH.
[0027] The processing compositions can also include one or more optional components that
are commonly used in black-and-white developing compositions, such as metal ion sequestering
agents, biocides (including fungicides), antifoggants, antioxidants, stabilizing agents
and contrast promoting agents. Such materials are known in the art, for example US-A-5,264,323,
US-A-5,299,362 and US-A-5,457,011. Useful stabilizing agents are α-ketocarboxylic
acids as described for example in US-A-4,756,997. Useful biocides include isothiazolines
such as 1,2-benzisothazolin-3-one, 2-methyl-4-isothiazolin-3-one, 2-octyl-4-isothiazolin-3-one
and 5-chloro-N-methyl-4-isothiazolin-3-one.
[0028] The developer solution may also contain a component to reduce or eliminate silver
sludge.
[0029] Preferably from 50 to 100% of the silver halide grains are spectrally sensitised.
In a particular embodiment of the invention, 100% of the silver halide grains are
spectrally sensitised.
[0030] The preferred range of silver:hydrophilic colloid ratio is 1-5, more preferably 1.5-3.5
and especially 2-3.
[0031] Preferably, the method of the invention is carried out in the presence of a density
enhancing amine compound. The density enhancing amine compound may be present in the
photographic material e.g. in the emulsion layer or an adjacent hydrophilic colloid
layer. Alternatively, the density enhancing amine compound may be present in the developer.
[0032] The amine density enhancing compounds are amines which when incorporated into a silver
halide material containing both spectrally sensitised and non-spectrally sensitised
silver halide grains cause a higher density to be obtained under the conditions of
development intended for the product.
[0033] In one embodiment of the invention the amine density enhancer is an amine which comprises
at least one secondary or tertiary amino group, and has an n-octanol/water partition
coefficient (log P) of at least one, preferably at least three, and most preferably
at least four, log P being defined by the formula:

wherein X is the concentration of the amino compound.
[0034] Preferably such an amine contains within its structure a group comprised of at least
three repeating ethyleneoxy units. Examples of such compounds are described in US
Patent 4,975,354. It is preferred that the ethyleneoxy units are directly attached
to the nitrogen atom of a tertiary amino group.
[0035] Included within the scope of the amino compounds which may be utilised in this invention
are monoamines, diamines and polyamines. The amines can be aliphatic amines or they
can include aromatic or heterocyclic moieties. Aliphatic, aromatic and heterocyclic
groups present in the amines can be substituted or unsubstituted groups. Preferably,
the amines are compounds having at least 20 carbon atoms.
[0036] In one embodiment the density enhancing amine has the general formula:
Y((X)
n-A-B)
m
wherein
Y is a group which adsorbs to silver halide,
X is a bivalent linking group composed of hydrogen, carbon, nitrogen and sulphur atoms,
B is an amino group which may be substituted, an ammonium group of a nitrogen-containing
heterocyclic group,
m is 1, 2 or 3 and
n is 0 or 1,
or the general formula:

wherein
R1 and R2 are each hydrogen or an aliphatic group, or R1 and R2 may together a ring,
R3 is a bivalent aliphatic group,
X is a bivalent heterocyclic ring having at least one nitrogen, oxygen or sulphur
atom as heteroatom,
n is 0 or 1, and
M is hydrogen or an alkali metal atom, alkaline earth metal atom, a quaternary ammonium,
quaternary phosphonium atom or an amidino group,
x is 1 when M is a divalent atom;
said compound optionally being in the form of an addition salt.
[0037] Preferred amino compounds for the purposes of this invention are bis-tertiary-amines
which have a partition coefficient of at least three and a structure represented by
the formula:

wherein n is an integer with a value of 3 to 50, and more preferably 10 to 50, R
4, R
5, R
6 and R
7 are, independently, alkyl groups of 1 to 8 carbon atoms, R
4 and R
5 taken together represent the atoms necessary to complete a heterocyclic ring, and
R
6 and R
7 taken together represent the atoms necessary to complete a heterocyclic ring.
[0038] Another preferred group of amino compounds are bis-secondary amines which have a
partition coefficient of at least three and a structure represented by the formula:

wherein n is an integer with a value of 3 to 50, and more preferably 10 to 50, and
each R is, independently, a linear or branched, substituted or unsubstituted, alkyl
group of at least 4 carbon atoms.
[0039] Particular amines suitable as density enhancers are listed in European Specification
0,364,166.
When the amine density enhancer is incorporated into the photographic material, it
may be used in amounts of from 1 to 1000 mg/m
2, preferably from 10 to 500 mg/m
2 and, especially, from 20 to 200 mg/m
2.
[0040] It is possible to locate the amine density enhancer in the developer rather than
in the photographic material.
[0041] The spectrally sensitised silver halide grains can be bromoiodide, chlorobromoiodide,
bromide, chlorobromide, chloroiodide or chloride.
[0042] The non-spectrally sensitised silver halide grains can be bromoiodide, chloroiodide,
chlorobromoiodide, bromide, chlorobromide, or chloride.
[0043] Both types of grain may also contain dopants as more fully described below.
[0044] Preferably both the spectrally sensitised and the non-spectrally sensitised grains
comprise at least 50 mole percent chloride, preferably from 50 to 90 mole percent
chloride.
[0045] The size of the latent image-forming and non-latent image-forming grains preferably
ranges independently between 0.05 and 1.0 µm in equivalent circle diameter, preferably
0.05 to 0.5 µm and most preferably 0.05 to 0.35 µm. The grain populations in the emulsion
layer may have the same or differing grain sizes or morphologies.
[0046] In one embodiment of the present invention the grain size of the non-spectrally sensitised
grains is smaller than that of the spectrally sensitised grains because, due to the
covering power of small grains, the required density may be obtained with less silver
halide.
[0047] As is known in the graphic arts field the silver halide grains may be doped with
Rhodium, Ruthenium, Iridium or other Group VIII metals either alone or in combination.
The grains may be mono- or poly-disperse. Preferably the silver halide grains are
doped with one or more Group VIII metal at levels in the range 10
-9 to 10
-3, preferably 10
-6 to 10
-3, mole metal per mole of silver. The preferred Group VIII metals are Rhodium and/or
Iridium.
[0048] In addition to graphic arts products the present materials may be black-and-white
non-graphic arts photographic materials needing moderate contrasts, for example, microfilm
and X-ray products.
[0049] The method of this invention can be used to process any suitable black-and-white
or color reversal photographic silver halide element. To process color reversal films
and papers, the black-and-white developing composition is generally used in the first
development step prior to treatment with a reversal bath and a color developing solution.
Such photographic elements and processes are well known in the art as described, for
example, in US-A-5,523,195.
[0050] Preferably, the method of this invention are useful to provide black-and-white images
in black-and-white films or papers, including radiographic films aerial films, industrial
films and graphic arts films as well as amateur and professional black-and-white films
and papers
[0051] The emulsions employed and the addenda added thereto, the binders, supports, etc.
may be as described in Research Disclosure Item 308119, December 1989 published by
Kenneth Mason Publications, Emsworth, Hants, United Kingdom.
[0052] The hydrophilic colloid may be gelatin or a gelatin derivative, polyvinylpyrrolidone
or casein and may contain a polymer. Suitable hydrophilic colloids and vinyl polymers
and copolymers are described in Section IX of Research Disclosure Item 308119, December
1989 published by Kenneth Mason Publications, Emsworth, Hants, United Kingdom. Gelatin
is the preferred hydrophilic colloid.
[0053] The present photographic materials may also contain a supercoat hydrophilic colloid
layer which may also contain a vinyl polymer or copolymer located as the last layer
of the coating (furthest from the support). It may contain some form of matting agent.
The vinyl polymer or copolymer is preferably an acrylic polymer and preferably contains
units derived from one or more alkyl or substituted alkyl acrylates or methacrylates,
alkyl or substituted alkyl acrylamides or acrylates or acrylamides containing a sulphonic
acid group.
[0054] The present emulsion layer is preferably formed by sensitising an emulsion with a
dye and then, if required, combining the spectrally sensitised emulsion with a non-spectrally
sensitised emulsion. Preferably the sensitising dye is chosen so that it does not
become desorbed from said spectrally sensitised grains.
[0055] Two emulsion components can be used where the first component is a "causer" emulsion
which is a normal i.e. chemically and spectrally sensitised component coated in the
range 10 to 100 %, preferably 50 to 100% by weight of the total silver laydown. The
requirements for the second "receiver" emulsion component are that it be clean, i.e.
free of fog, and be capable of being developed by the enhanced co-development process.
[0056] The lower dye laydown which is possible using this invention is also particularly
advantageous for systems which have been designed to run under low replenishment rate.
Under normal replenishment rates (typically 300 - 600mls/m
2 ) there is sufficient overflow of solution to carry out the build up of dye products
released into the solution. If these dye products are not bleached by the chemistry
then under low replenishment (300ml/m
2 and below) the residual dye builds up to unacceptable levels causing dye stain on
the materials being processed. This problem can be effectively eliminated or reduced
by removing the need for the usual amounts of dye.
[0057] Where a particular spectral sensitisation requires the use of compounds not necessary
in the other emulsion components of the coating, the laydown of these compounds may
be reduced. This reduction will lead to cost savings. These compounds may further
have undesirable properties, such as high post-process UV Dmin, and their effect can
be reduced.
[0058] As the speed of the non-spectrally sensitised emulsion is not critical to the final
photographic speed of the coated product this emulsion does not require chemical sensitisation
and thus the production of this component requires fewer steps in the manufacturing
process and less stringent quality control leading to manufacturability and cost benefits.
[0059] As the maximum density of the material is not primarily dependant upon latent image-forming
grains, the invention has the advantage that imaging emulsions of grain size above
those used in standard high contrast coatings can be used without the need to increase
the overall silver laydown.
The sensitising dye may have one of the general formulae:

wherein
R8, R9 and R10 represent an alkyl group which may be substituted, for example with an acid water-solubilising
group, for example a carboxy or sulpho group,
R11 and R12 are an alkyl group of 1-4 carbon atoms,
R13, R14 and R15 represent H, substituted or unsubstituted alkyl or substituted or unsubstituted aryl,
and
X is a halogen, for example chloro, bromo, iodo or fluoro.
[0060] The present photographic materials preferably contain an antihalation layer on either
side of the support. Preferably it is located on the opposite side of the support
from the emulsion layer. In a preferred embodiment an antihalation dye is contained
in the hydrophilic colloid underlayer. The dye may also be dissolved or dispersed
in the underlayer. Suitable dyes are listed in the Research Disclosure mentioned above.
[0061] The light-sensitive silver halide contained in the photographic elements can be processed
following exposure to form a visible image by associating the silver halide with an
aqueous alkaline medium in the presence of the ascorbic acid developing agent contained
in the medium or the element.
[0062] The present photographic materials are particularly suitable for exposure by red
or infra-red laser diodes, light emitting diodes or gas lasers, e.g. a Helium/Neon
or Argon laser.
[0063] The invention is further described by way of example in the Examples given below.
Example 1
[0064] A polyethylene terephthalate film support (with an antihalation pelloid layer) was
coated with an emulsion layer consisting of a spectrally sensitised emulsion and a
non-spectrally sensitised emulsion, an interlayer, and a protective supercoat. The
supercoat was a standard formula containing matte beads and surfactants and was coated
at a gel laydown of 0.49 g/m
2. The interlayer contained the amine density enhancer compound of the formula:
(C
3H
7)
2N(CH
2CH
2O)
14CH
2CH
2N(C
3H
7)
2
and a latex copolymer and was coated at a gel level of 1.0 g/m
2.
[0065] The emulsion substrates used for the dyed and undyed components were not the same.
The dyed component consisted of a 70:30 chlorobromide cubic monodispersed emulsion
(0.21 µm edge length), whereas the undyed component consisted of a 70:30 chlorobromide
cubic monodispersed emulsion (0.18 µm edge length) . Their silver laydowns were 1.98
and 1.32 g Ag/m
2, respectively, giving a total silver laydown of 3.30 g Ag/m
2. Both were suitably chemically sensitised with a 10 minute digestion at 65°C . The
dyed emulsion contained a sensitising dye giving a broad response between 630 and
670 nm, potassium iodide and a suitable anti-foggant package. The undyed emulsion
contained no dye, potassium iodide and a suitable anti-foggant package. The total
gel laydown of the emulsion layer was 1.21 g/m
2, and the silver:gelatin ratio was 2.73.
[0066] In order to aid the coating of this relatively low gelatin coating a conventional
thickening agent was added to increase melt viscosity and to give acceptable coating
quality. The dyed emulsion melt was kept separate from the undyed emulsion melt until
they were mixed in line immediately before the coating hopper.
[0067] The above coating was evaluated by exposing through a 0.1 increment step wedge with
a 10
-6 flash sensitometer fitted with a red light WRATTEN™ 29 filter and then processed
in KODAK™ RA2000 Developer (diluted 1+2), which had been adjusted to a pH of 10.5,
at 35°C for 30 seconds. After development, the coating was fixed, washed and dried.
The commercially available rapid access film KODAK™ PAGI-SET HN film was exposed and
processed likewise, as was the commercially available nucleated film KODAK™ RECORDING
2000 HN film. The exposing and processing steps of all three films were repeated in
the same developer after adjustment of the pH to 10.0 and to 9.5.
[0068] The same three films were exposed in a like manner and then processed at 35°C for
30 seconds in an ascorbic acid-based developer with the following formula:
Table 1
Component |
Amount for 1 litre |
Water |
600.0 g |
Potassium sulphite solution (45% w/w) |
44.0 g |
Potassium hydroxide solution (45.5% w/w) |
5.0 g |
Dimezone-S |
2.0 g |
L-Ascorbic acid |
35.0 g |
Sodium bromide |
3.8 g |
VERSANEX™ 80 |
10.0 g |
IRGAFORM™ 3000 |
3.25 g |
Benzotriazole |
0.20 g |
Potassium carbonate |
100.0 g |
|
|
pH adjust to |
10.5 |
Water to |
1 litre |
[0069] The exposing and processing steps were repeated after the developer had been adjusted
to a pH of 10.0, and to a pH of 9.5. The sensitometric results for processing in RA2000
(1+2) are shown in Figures 1 to 3 with selected sensitometric parameters shown in
Table 2. Likewise, the sensitometric results for processing in the ascorbic acid-based
developer are shown in Figures 4 to 6 with selected sensitometric parameters in Table
3.
Table 2
Film |
pH |
Speed (D = 0.6) |
Midscale Contrast |
D-max |
Enhanced Co-Development |
10.5 |
1.44 |
6.67 |
5.80 |
10.0 |
+0.04 |
+1.37 |
-0.04 |
9.5 |
+0.21 |
+3.11 |
-0.34 |
KODAK™ PAGI-SET HN |
10.5 |
1.40 |
4.62 |
5.57 |
10.0 |
-0.02 |
+0.01 |
-0.04 |
9.5 |
-0.05 |
-0.69 |
-1.29 |
KODAK™ RECORDING 2000 HN |
10.5 |
1.57 |
9.35 |
5.69 |
10.0 |
-0.16 |
-3.76 |
-2.46 |
9.5 |
-0.21 |
-5.66 |
-2.46 |
Table 3
Film |
pH |
Speed (D = 0.6) |
Midscale Contrast |
D-max |
Enhanced Co-Development |
10.5 |
1.46 |
6.44 |
5.92 |
10.0 |
+0.01 |
+0.33 |
-0.05 |
9.5 |
+0.06 |
+0.31 |
-0.22 |
KODAK™ PAGI-SET IN |
10.5 |
1.44 |
4.40 |
5.53 |
10.0 |
-0.04 |
-0.01 |
-0.02 |
9.5 |
-0.07 |
-0.32 |
-0.13 |
KODAK™ RECORDING 2000 HN |
10.5 |
1.62 |
8.42 |
5.90 |
10.0 |
-0.13 |
-1.22 |
-0.13 |
9.5 |
-0.26 |
-5.31 |
-2.92 |
[0070] The data in italics in Tables 2 and 3 at pH 10.0 and pH 9.5 indicate the sensitometric
change from pH 10.5.
[0071] In RA2000 (1+2) (Table 2) it will be noted that both commercially available films
show deterioration in sensitometry as the pH is changed to 10.0 and 9.5 from 10.5.
The enhanced co-development film shows the best stability, especially in terms of
midscale contrast and D-max, but the significant gain in speed (0.21 log E) on going
from pH 10.5 to 9.5 is undesirable.
[0072] Processing in the ascorbic acid-based developer (Table 3) provides very stable sensitometry
over the pH range 10.5 to 9.5 for the enhanced co-development film. This is desirable
as it implies that a minimum of processor control is required for the combination
of the invention. The nucleated film gave a loss of contrast on going from pH 10.5
to 10.0, and a large loss in D-max from pH 10.0 to 9.5. Although the rapid access
film was moderately stable over the pH range, it should be noted from Figure 5 that
the upper scale contrast sagged at pH 9.5. The enhanced co-development film and ascorbic
acid-based developer combination showed distinct advantages over the rapid access
film, and over the enhanced co-development film and hydroquinone-based developer combination,
in terms of contrast, D-max, photographic speed and processing stability.
Example 2
[0073] Samples of the enhanced co-development film of the invention, KODAK™ PAGI-SET HN
film, and KODAK™ RECORDING 2000 HN film were exposed on a Linotronic 330 imagesetter
(a helium-neon (HN) exposing device manufactured by LINOTYPE HELL™). The films were
exposed to an image containing areas of text, D-max and D-min, as well as half-tone
dots of various sizes over the range 1 to 99%. For each film sample the image was
repeated a number of times (25) so as to obtain a "sweep" of exposures such that at
one end of the galley the film was underexposed while at the other the film was overexposed.
[0074] The exposed films were developed in both RA2000 (1+2) and the ascorbic acid-based
developer of Example 1 above, at pH 10.5, 10.0 and 9.5, at 35°C for 30 seconds. Each
exposure patch was read for D-max and size of the 50% dot, using an X-RITE™ 361T densitometer.
A particular note was made of the imagesetter exposure value on each galley where
the 50% dot read as a 55 to 60% dot, providing that the D-max was at least 4.2.
[0075] Each film sample was then contacted on to KODAK™ CONTACT 2000 CA4 general purpose
contact film using a KODAK™ 2800 contact frame. The contacts were developed in RA2000
(diluted 1+4) at 35°C for 30 seconds. The dot size corresponding to the galley patches
of interest were read and compared to the theoretical dot size that might have been
expected, assuming no dot gain. (Half tone dots which are "soft" give a larger dot
gain on contacting than dots which are "hard". It is accepted that the best image
quality and tone reproduction is provided by "hard" dot films.) The results of this
test are summarised in Tables 4 and 5, for the RA2000 (1+2) and ascorbic acid-based
developers, respectively.
Table 4
Film |
pH |
Dot Size |
Contacting |
|
|
|
Theory |
Found |
Dot Gain |
Enhanced Co-Development |
10.5 |
56.0% |
44.0% |
46.6% |
2.6% |
10.0 |
59.2% |
40.8% |
44.1% |
3.3% |
9.5 |
60.4% |
39.6% |
45.4% |
5.8% |
KODAK™ PAGI-SET HN |
10.5 |
57.1% |
42.9% |
47.0% |
4.1% |
10.0 |
56.7% |
43.3% |
47.5% |
4.2% |
95 |
-* |
-* |
-* |
-* |
KODAK™ RECORDING 2000 HN |
10.5 |
55.0% |
45.0% |
46.4% |
1.4% |
10.0 |
-* |
-* |
-* |
-* |
9.5 |
-* |
-* |
-* |
-* |
* A dash in Tables 4 & 5 indicates that no satisfactory practical exposure was obtained. It will be seen from the data presented in Table 4 for development in a conventional
hydroquinone-based developer that, at pH 10.5, dot gains typical of the three film
types were given, viz. a "soft" dot for the rapid access material, a "hard" dot for
the nucleated material and an intermediate dot quality ("semi-hard" dot) for the enhanced
co-development film of the invention. As the pH of the hydroquinone-based developer
is lowered, so it becomes increasingly difficult to obtain a satisfactory result in
terms of a mid-tone dot for a density greater than or equal to that required for acceptable
contacting (D at least 4.2). At pH 9.5 the enhanced co-developer photographic material
is the only one to give a practical result from the imagesetter exposures, although
it will be noted that the dot gain has grown to unsatisfactory proportions (5.8%). |
Table 5
Film |
pH |
Dot Size |
Contracting |
|
|
|
Theory |
Found |
Dot Gain |
Enhanced Co-Development |
10.5 |
56.4% |
43.6% |
46.5% |
2.9% |
10.0 |
57.5% |
42.5% |
44.8% |
2.3% |
9.5 |
59.9% |
40.1% |
43.0% |
2.9% |
KODAK™ PAGI-SET HN |
10.5 |
57.8% |
42.2% |
45.9% |
3.7% |
10.0 |
57.4% |
42.6% |
47.3% |
4.7% |
9.5 |
59.6% |
40.4% |
45.5% |
5.1% |
KODAK™ RECORDING 2000 HN |
10.5 |
59.7% |
40.3% |
42.6% |
2.3% |
10.0 |
54.9% |
45.1% |
46.8% |
1.7% |
9.5 |
-* |
-* |
-* |
-* |
* A dash in Tables 4 & 5 indicates that no satisfactory practical exposure was obtained. It will be seen from the data presented in Table 4 for development in a conventional
hydroquinone-based developer that, at pH 10.5, dot gains typical of the three film
types were given, viz. a "soft" dot for the rapid access material, a "hard" dot for
the nucleated material and an intermediate dot quality ("semi-hard" dot) for the enhanced
co-development film of the invention. As the pH of the hydroquinone-based developer
is lowered, so it becomes increasingly difficult to obtain a satisfactory result in
terms of a mid-tone dot for a density greater than or equal to that required for acceptable
contacting (D at least 4.2). At pH 9.5 the enhanced co-developer photographic material
is the only one to give a practical result from the imagesetter exposures, although
it will be noted that the dot gain has grown to unsatisfactory proportions (5.8%). |
[0076] In comparison, when the enhanced co-developer film and ascorbic acid-based developer
are used in combination, across the whole pH range 10.5 to 9.5, excellent dot quality
was achieved. The comparison films behaved less satisfactorily: by a pH of 9.5 the
rapid access film had started to give an unacceptable dot gain (5.1%), and the nucleated
film had failed to provide acceptable densities. Hence, the combination of film material
and developer of the invention provides a route to high quality "semi-hard" dots in
conditions demonstrated to be unfavourable for films and developers of the known art.
Example 3
[0077] The imagesetter-exposed and processed samples of Example 2 were examined by means
of a NIKON™ binocular microscope connected to a COHU™ high performance CCD camera.
The areas chosen for examination were the 50% written half-tone dots used for the
contacting tests. Each patch was viewed and focused using a television monitor, and
a digital image captured using an ADVICE™ image analysis system (Brian Reece Scientific
Ltd).
[0078] Side by side comparisons of the images were then made. The results obtained for the
enhanced co-developer film in both the hydroquinone-based and ascorbic acid-based
developers at pH 10.0 and at pH 9.5 are reproduced as Figures 7 to 10.
[0079] It will be seen from Figure 7 that a low level of developed background silver speckle
is apparent in the unexposed regions of the enhanced co-developer film when a hydroquinone-based
developer is employed at a pH of 10.0. The corresponding ascorbic acid-based developer
at pH 10.0 shows no sign of developed speckle (Figure 8).
[0080] Furthermore, at pH 9.5, an undesirable level of developed speckle is given in RA2000
(1+2) (see Figure 9), whilst at the same pH hardly any speckle is developed in the
ascorbic acid-based developer (Figure 10).